Conventional methods of producing heating, including burning fossil fuels and electric resistance heat generation, have disadvantages of increasing operating costs and low energy efficiency. Heat pumps provide an improvement over these methods.
Heat pumps extract low temperature heat from some available source through evaporation of a working fluid at an evaporator, compress the working fluid vapor to higher pressures and temperatures and supply high temperature heat by condensing the working fluid vapor at a condenser. Residential heat pumps use working fluids such as R410A to provide air conditioning and heating to homes. High temperature heat pumps using either positive displacement or centrifugal compressors use various working fluids, such as HFC-134a , HFC-245fa and CFC-114, among others. The choice of working fluid for a high temperature heat pump is limited by the highest condenser operating temperature required for the intended application and the resulting condenser pressure. The working fluid must be chemically stable at the highest system temperature and it must generate a vapor pressure at the maximum condenser temperature that does not exceed the maximum allowable working pressure of available equipment components (e.g. compressors or heat exchangers). The working fluid must also have a critical temperature higher than the maximum targeted condensing temperature.
Increasing energy costs, global warming and other environmental impacts, in combination with the relatively low energy efficiency of heating systems that operate by fossil fuel combustion and electrical resistance heating make heat pumps an attractive alternative technology. HFC-134a, HFC-245fa and CFC-114 have high global warming potential and CFC-114 also has impact on ozone depletion. There is a need for low global warming potential, low ozone depletion potential working fluids for use in high temperature heat pumps. Fluids that enable operation of existing heat pump equipment designed for HFC-134a at higher condenser temperatures while still attaining an adequate heating capacity would be particularly advantageous.